PHILADELPHIA -- Blue Jays manager Cito Gaston was pulled away from his pregame meeting with reporters on Tuesday, called back into the clubhouse for an impromptu meeting with head trainer George Poulis. Another one of Toronto's pitchers had suffered an injury.

On Wednesday, right-hander Casey Janssen was placed on the 15-day disabled list with inflammation in his throwing shoulder -- the same one that required surgery two springs ago and cost him all of last season. The Blue Jays have promoted lefty Brad Mills to take Janssen's turn in the rotation on Thursday in Philadelphia.

Losing Janssen is the latest blow to a pitching staff that has been riddled with health woes.

Ace Roy Halladay is currently fighting a strained right groin and closer Scott Downs is scheduled to undergo an MRI on Wednesday after exiting Tuesday's game in the 10th inning with a left foot issue. On Friday, starter Jesse Litsch underwent season-ending Tommy John ligament-replacement surgery on his right elbow.

These are only the recent setbacks. Toronto also opened the season without right-handers Shaun Marcum (right elbow) and Dustin McGowan (right shoulder). There is a slim chance that Marcum and McGowan could make appearances late in the season, but it's more likely that they'll join Litsch as options for some time during the 2010 campaign.

This past spring, the 24-year-old Mills -- selected in the fourth round of the 2007 First-Year Player Draft by the Blue Jays -- was in a position to claim a starting job on the Opening Day roster. The losses of Marcum and McGowan, along with having A.J. Burnett sign with the Yankees as a free agent, opened the door for Mills to compete for a role with the big league club.

Down the stretch in Spring Training, rookies Ricky Romero and Scott Richmond claimed the final two spots in the rotation and Mills opened the season with Triple-A Las Vegas. In 13 games with Las Vegas, Mills posted a 1-8 record with a 4.48 ERA, 65 strikeouts and 34 walks over 76 1/3 innings. Mills will be the 11th different starter and fifth rookie to make a start for Toronto this year.

At the beginning of the spring, Janssen was a top candidate for a rotation job with the Jays, but he suffered a setback in his return from shoulder surgery in March. Janssen was called up to Toronto at the end of May and has had inconsistent results, going 2-3 with a 6.23 ERA in five starts. Prior to this year, Janssen last pitched in the Majors in '07, when he posted a 2.35 ERA in 70 games out of the bullpen.